hughson



March 9, 1965 J. D. HUGHSON 3,172,627

CAB SIGNAL RECEIVING SYSTEM FOR RAILROADS Filed Dec. 2, 1960 3Sheets-Sheet 1 TRAFFIC DIRECTION H I2 5:} i TRACK RAIL\S I '2: f'r

l4 II TRACK CURRENT l5 l6 l7 CODING APPARATUS FILTER AND SATURABLE(TRANSMITTER) AMPLIFIER REACTOR RECT'F'ER fiCR l8 W l9 DECODINGLOCOMOTIVE APPARATUS CONTROL AND DISPLAY FIG. 2. n I +5 W 48 EJ525122 wI I6 36 40 42 1 46 E/ I E I 5O 2O v I? I 2 2 J CR .iLJ L DECODING o 3 29APPARATU I i. H 4 L I CONTROL AND DISPLAY a APPARATUS 9 INVENTOR. gJ.D.HUGHSON l4 'I/l/I; Jill/I SECTION 2-2 FROM FIG. I.

HIS ATTORNEY March 9, 1965 o. HUGHSON CAB SIGNAL RECEIVING SYSTEM FORRAILROADS BY HIS ATTORNEY March 9, 1965 J. D. HUGHSON 3,172,627

. CAB sxcmu. RECEIVING SYSTEM FOR RAILROADS Filed Dec. 2, 1960 3Sheets-Sheet 3 FIG. 4.

A INPUT VOLTAGE TO AMP.

r' 1'? r' B OUTPUT V V \7 VOLTAGE OF AMP. 22

c ,i ,1 OUTPUT V V V VOLTAGE OF AMP 23 II 1 D A COMBINED VOLTAGE OUTPUTFROM AMPS. 22 AND 23 FLUX CHANGE IN CORE :6

IN V EN TOR.

J.D.HUGHSON HIS ATTORNEY United States Patent ce 3l7zfiz7 Patented Mau'.9, 1965 Heretofore, each receiving coil was connected to a sep-3,172,627 .arate amplifier so that a distinct channel was made avail-CAB SIGNAL SYSTEMFOR able on the output side for each induced trackcurrent in J. Donald Hughson, Rochester, N.Y., assignor to GeneralSignal Corporation Filed Dec. 2, 1964), Ser. No. 73,434 9 Claims. (Cl.246-63) This invention relates to railway signaling systems, and moreparticularly pertains to the vehicle-carried receiving apparatus forwhat is commonly known as a continuous inductive coded type system.

In such continuous inductive type systems it is common practice toclassify these with respect to the method of transferring the signal tothe moving vehicle and the kind of signal being transmitted through thetrack rails. This invention is limited to a continuous inductive codedA.C. type system in which the transmitted signals are continuouslyavailable through an inductive coupling on the moving locomotive andthese same transmitted signals in the rails are time spaced coded groupsof constant a. plitude A.C. voltages. The transmitted groups of theseAC. voltages may be said to be coded since their frequency is usuallyindicative of the signal indication at the forward end of the blocktoward which the train is moving.

The cab receiving apparatus makes it possible to provide a continuouscontrol and display in a locomotive cab concerning the tralficconditions on the track ahead. Essentially, this is accomplished byapplying pulses of electrical energy at distinctive coding rates to thetrack rails at the exit end of each block which may involve one or moretrack sections. These pulses travel along the track rails toward thetrain and induce voltages in receiving coils mounted on the locomotiveand positioned over each track rail ahead of the leading wheels. Thetraincarried equipment amplifies the induced voltage pulses and detectstheir rate of occurrence. Since the particular coding rate in effect atany time corresponds to the trafiic conditions ahead, it becomespossible to provide one of a number of different cab signal aspects tothe train operator which reflect existing trafiic conditions.

As in all signaling systems for railroads, it is imperative that highstandards of reliability and fail-safe operation are designed into thesystem. The receiving apparatus, since it is carried on the movingvehicle, is highly subject to mechanical shock, and therefore, should bedesigned to withstand considerable abuse in this respect. Also, thisapparatus must be extremely sensitive to rail currents, since themagnetic coupling is relatively loose because of rail clearancerequirements which allow only minute voltages to be induced into thepick-up or receiving coils. These receiving coils are generally mountedforward of the most forward wheels and axle of the locomotive anddisposed over each rail so that they will inductively couple with therail currents, and thereby be effective to act as the secondary of atransformer; the rails themselves, with the rail currents flowingtherein, act as the primary of this transformer. Substantially,shockproof amplifiers have previously been designed to overcome theseobstacles; however, other considerations are of some consequence. Onlyrail currents, one in each rail, which are in phase, and no others, mustbe capable of signaling a particular train. Under certain-conditionswherein one-track circuit may have a high resistance due to a highresistance bond or an open bond, stray track currents from an adjacenttrack may have a substantial infiuence on the amplifiers, andconsequently their output will most likely produce a false indication.Failings within the receiving apparatus itself may also produce falsecab indications, if these are not in some way prevented.

each receiving coil. This output, in one instance, was directed to atwo-phase relay to insure proper phasing of the induced track currentsand to prevent operation if only one of the two channels of inducedtrack currents were available after amplification, possibly due .to .anopen circuit in the other channel. The amplified induced track currentswere arbitrarily displaced in phase so that both, when recombined in theproper phase relationship, would operate a relay, but neither alonewould operate this electromagnetic device. The major disadvantage of thetwo-phase relay is that it will not respond to the frequency of theusual track code pulses because its armature is too sluggish. Otherdisadvantages of the two phase relay are that it is large, heavy, andexpensive. Another scheme to insure that the track currents are inproper phase relationship used a coincidence gas discharge tube to gateboth in-phase track currents to the output circuits. The disadvantage ofthe coincidence tube and the other required associated electron tubes isthat it is no more shock-proof than any other electron tubeconfiguration.

t is with the aim of preventing any false indication or control to thelocomotive that my invention is particularly directed. The saturablereactor in the embodiment of this invention is a more desirablesubstitute for either the two phase relay or a coincidence vgatingelectron tube for it is fast in response, small, light in Weight,inexpensive, and rugged in structure for operability under extreme shockconditions.

The feed for this saturable reactor is obtained from two separatelychanneled amplifiers, each of which clips one-half of the oppositelypolarized portions of the cur rent waveform and later combines each halfin successive phase relationship to reform a complete in-phase Waveform.The application of each half of the waveform to separate halves of theprimary of the saturable reactor saturates the core first in onedirection, then the other, under normal operating conditions. If onerail current becomes nullified by another stray leakage rail currentfrom an adjacent track, or if one of the amplifiers should become opencircuited, this loss of one-half of the output waveform would beeflective to saturate the core of the reactor in one direction onlywhere it would remain, thereby providing no output. Under anothersituation if a short circuit appeared in one channel of the amplifierand thereby produced a large DC. current through .onehalf of the primaryof the reactor this would hold the magnetization of the core at thesaturation level and thereby again act as a gating device to produce no.output. Likewise, under ditferent circumstances, whenonechaunel isproducing a weak signal output, then no saturation will result on itspolarity direction of magnetization, but the other channel will actnormally and saturate the core to it's polarity direction therebysticking it, for the weak signal will be insuificient to reverse themagnetization to the other direction.

In view of the above, one object of this invention is to provide areliable and fail-safe signal receivingsystem for railroad locomotives.7

Another more specific objectis toprovide a method for through gating theamplified track currents when each is normally operating.

Another object is to provide a cut off gate for the track currents wheneither one or .the other channel is lacking.

Another object is to provide a cut off gate for Vt-he' V amplified trackcurrents when either one or the other channel is short circuited. k 1

Another object is to provide a cut off gate for the amplified trackcurrents when either track current functions in out of phaserelationship with the other.

Other objects, purposes and characteristic features of this inventionare in part obvious from the accompanying drawings and in part pointedout as the description of the invention progresses.

In describing this invention in detail reference will be made to theaccompanying drawings illustrating one specific embodiment of thisinvention and in which:

FIG. 1 represents a block diagram of the overall code communicationsystem;

FIG. 2 shows a typical circuit arrangement for the receiving coils,filter, amplifiers, saturable reactor, and a block diagram of thedecoding apparatus and control and display equipment;

FIG. 3 illustrates a group of waveforms representing normal operation ofthe system for a period of time and later shows the efiect of an opencircuit on this normal operation; and

FIG. 4 shows waveforms that illustrate how the saturable reactor willfunction as a cut off gate when the track currents are out of phase.

To simplify the illustration and facilitate the explanation of thisinvention various parts and circuits have been shown diagrammatically.Certain conventional illustrations have been used and the drawings havebeen made to make it easier to understand the principles and manner ofoperation rather than to illustrate the specific construction andarrangements of parts that might be used in practice. The symbols andindicate the opposite terminals of a suitable source of direct currentpower or may also be used to indicate instantaneous polarities appearingon certain conductors. The symbols +B and ground are used to indicatethe positive and negative terminals of the energy source respectivelyfor electron tube potentials.

Apparatus It will be noted by referring to FIG. 1 that the track currentcoding apparatus along the wayside for applying coded train controlenergy to the track rails has not been shown in detail since it may beof the type shown, for example, in the patent to T. J. Judge No.2,141,535 granted on December 27, 1938. This wayside apparatus 10provides means, as in Judge above, for placing alternating current of afrequency different from the usual commercial frequencies, such as 100cycles per second, on the track rails in coded form constituted byinterrupting the current periodically at various rates. The particularcodes involved in the usual system are those having a rate of 180, 120and 75 interruptions per minute. The system is so arranged that a trainin a block immediately to the rear of an occupied block will receive aconstant uninterrupted alternating current having no coding rate, which,in turn, will display the most restrictive indication in the locomotivecab; one in the second block to the rear of the occupied block willreceive the 75 code rate or a less restrictive indication; in the thirdblock to the rear of the occupied block the 120 code rate or a stillless restrictive indication, and in the fourth block to the rear and allthe blocks to the rear thereof the 180 code rate or a clear indication.In different systems and/ or under different conditions within the samesystem there may be various assignments of code rates to the blocksother than the above, for example, two successive blocks may receive the120 code rate.

The transmission line in this communication system consists of one trackrail 12, the most forward wheels and axle of the locomotive 13, and theother track rail 14.

The usual receiving apparatus may be thought of as comprising the filterand amplifier 15, the rectifier 17, the code responsive relay CR (or amaster relay MR), decoding apparatus 18, and control and displayapparatus 19. In former systems either a two phase relay or acoincidence gate comprising gas discharge tubes was used between thefilter and amplifier 15 and rectifier 17 to insure that only properlyphased currents would operate the rectifier 17. In this system asaturable reactor 16 is used for this purpose.

It is common practice to use pick-up or receiving coils 11 and 11, whichare also an essential part of the receiving equipment, one over eachrail to separately drive an amplifier, which, in turn, feeds one phaseof a two phase relay. Thus each receiving coil must be receiving asignal of the proper phase and each amplifier must be working at theproper level in order to obtain proper operation of this two phaserelay. The main disadvantage of this type relay is its failing torespond to the codes in a coded track system because of its inherentsluggish response. This last restriction limits the number of availableindications to the very minimum, whereas the saturable reactor possessesa rapid response characteristic and therefore can readily respond to thetrack code pulses.

In the filter and amplifier 15 tuning circuits are arranged in theadvance portion to pass the cycle per second energy and exclude theusual commercial power frequencies such as 25, 50 and 60 cycles. In theembodiment of this invention two such filters are arranged, one for eachreceiving coil. The output of the filter feeds a class A amplifier whichinverts the signal but maintains the same waveform as the input. Theelectron tubes 20 and 21 shown in FIG. 2 represent this class Aamplifier. The output of this amplifier feeds a class B push-pullamplifier embodied in electron tubes 22 and 23 which eliminates thepositive-going half of the waveform and at the same time again invertsthe input waveform. The output of this class B amplifier then has thesame wave form except for the half which is eliminated as was providedfrom the output of the filter. When each of these half waves are addedback-to-back or in phase relationship in the respective primary windings24 and 25, they will combine to form a complete sine wave, thereforeeach channel makes up each half of this continuous sine wave which nowappears as an in-phase voltage.

The saturable reactor 16 is designed in such a manner so that its corewill readily saturate by each of the peak voltages which are applied toeach half of the primary windings 24 and 25. The secondary winding 26connects to a detecting device, such as the rectifying bridge 27 so thatthe rectified output from this bridge may be used to operate the coderesponse relay CR. Inasmuch as this unit is a saturable reactor, theonly time a voltage will be induced into the secondary winding is duringthe time of a change of flux in the core. Such flux changes will beconsidered later when the operation under various conditions isdiscussed in detail. The core of this saturable reactor possesses amagnetic material such that its characteristic is what is commonly knownin the art as a rectangular hysteresis loop.

To simplify the explanation of this receiving system hereinafter, thesignals will be terminated at the code responsive relay CR, for it ishere at this relay, when it ceases to function at any of the transmittedcoding rates, that the cab indication will go to a stop display, and insome systems may further apply the brakes to the locomotive, thislatter, usually after some time delay.

The decoding apparatus 18 is required to accept the coded message andtransform it into a control and/ or display signal which can be acceptedby the locomotive control and display apparatus 19. It should beunderstood that the decoding apparatus 18 per se is not a part of thisinvention but is required to complete the system. For this reason thisapparatus is not shown in detail for it is similar to that shown inPatent No. 2,731,553 by F. P. Zaifarano et al. on a Coded Cab SignallingSystem for Railroads dated January 17, 1956.

The locomotive control and display apparatus 19 may take on manydifferent forms. One possible combination is as shown in detail by W. H.Reichard et al., in

' around the circuit shown in FIG. 2.

Patent No. 2,223,131 dated November 26, 1940, for example.

Operation The operation of this system evolves more specifically In thelower portion of this figure a mechanical section 2-2 is taken from FIG.1 of the cross section of the rails 12 and 14. Let us start thisdiscussion with the assumption that the instantaneous rail current inany one of the pulse groups is flowing toward the reader in rail 12,which is designated by a dot, and the current in rail 14 is flowing awayfrom the reader, indicated by a sign. This is a normal condition ofthese track currents, for at some instant the current (see FIG. 1) willbe flowing from the transmitter 159, through track rail 12, through themost forward wheels and axle 13 of the locomotive, and return to thetransmitter it via rail 14.

On each side of the locomotive, receiving coils 11 and 11' are disposedabove rails 12 and 14 respectively, so that the magnetic material withinthese coils forms a portion of a magnetic circuit with respect to eachof the track currents flowing in the rails. Each of these receivingcoils may be thought of as the secondary of a transformer which hasmultiple turns on the secondary, whereas the primary is simply a partialsingle turn formed by each of the two rails. If the current is flowingas indicated in rail 12 and is increasing in magnitude a voltage will bedeveloped across coil 11 having a positive polarity on wire 34? and anegative polarity on wire 31. Similarly, the current flowing in rail 14in the direction indicated when increasing will produce a positivepolarity on wire 32. and a negative polarity on wire 33. Connectedacross each of these coils is a momentary shorting switch 28 and 29which may be used to momentarily short-circuit each input to determinewhether the remaining circuitry is working properly. More will bediscussed about this feature later during the discussion of variousmodes of operation.

The next apparatus involved in this circuitry is the filter 34 which isa portion of the filter and amplifier shown .in FIG. 1. Each of thevoltages generated across a .receiving coil are applied to each input ofthis filter 3 through a series capacitor 36 and 37 respectively. Thevoltage from receiving coil 11 will cause a current to how through theprimary winding .38 in an upward direction or away from groundpotential, whereas the voltage induced in coil 11' will cause thecurrent to flow through primary winding 39 also in an upward directionbut to ward ground potential. The combination of capacitor 36 andwinding 38, and capacitor 37 and winding 39 are respectively tuned to afrequency of 100 cycles per secend, which is the same frequency beingtransmitted through the track rails; consequently, this filter isdesignated to accept maximum energy at this frequency. The transformers4i and 41 within the filter transfer the energy to the grid circuits ofthe class A amplifier tubes and 21. The secondaries of thesetransformers 42 and 43 are each tuned by a parallel capacitance 44 and45 respectively. If we now assume that the transformers are connected inphase (note dot polarity indications) rather than 180 out of phase, thenthe secondary side of the transformer at the potential progressingfarther above ground will be connected so that a positive-going pulsewill appear at this instant on the coupling capacitor 45. Similarly, atthis same instant, a ne ative-going pulse will appear at the couplingcapacitor 47 in the opposing circuit. The sine voltage waveforms areshown in FIG. 2 which are applied to the grids of tubes 26 and 21. Notethat these are 180 out of phase.

The electron tube 20 and 21 are typical class A amplifiers biased abovecut-off by resistors 59 and 51 respectively, and therefore, aswell-known in the art, the output voltage waveforms appearing at theplates of these tubes 6 will be complete waveforms of the input but oneof phase by 180. These voltages are, in turn, applied through couplingcapacitors 48 and 49 to the grids of the class B amplifier tubes 22 and2.3 respectively.

It is also well-known in the art that since aclaSs B amplifier is biasedat cut-off, in this instance by the batteries 52 and 53, it will clipthe positive-going portion of the output voltage waveform. Therefore,since the phase relationship is again inverted by 180 through thisamplifier a negative-going waveform will appear at the output of tube23. After a half cycle the remainder of this waveform will be clipped;however, at this time tube 22 is about to produce a negative-goingwaveform because of the phase relationship of the voltage applied to itsgrid, whereas during the first half of the cycle its output voltagewaveform had been clipped.

The output of each class B amplifienboth of Whichare arranged inpush-pull fashion, is connected to each half of the primary winding ofthe saturable reactor 16. Assuming that a positive-going pulse producesa current from plate to cathode within the class B amplifier a currentwill flow in winding 25 from the battery to the plate of tube 23. Thiscurrent flow may be represented by the direction of the arrow adjacentto this winding 25. Similarly, during the next cycle the current willflow in winding 24 in the direction of the arrow shown adjacent to thiswinding. Let us assume that the arrow in an upward direction saturatesthe core to a positive condition or flux density, whereas an arrow inthe downward direction produces a saturation in the core in a negativedirection or negative flux density. When each of these class Bamplifying tubes are operated first one, then the other, in proper timerelationship, then the core will be saturated first to a negative state,and alternately to a positive state within the course of each cycle.

In any transformer a change in flux density within the core produces anoutput voltage on the secondary side such as within winding 26. Thisinduced voltage in the secondary may be rectified by a typical bridgerectifier such as 17, which, in turn, may be used .to operate the coderesponsive relay CR. In some systems this same relay is designated as amaster relay MR, but the function of this MR relay substantially thesame as that of the CR relay. At a frequency of cycles per second theinductive reactance of either the CR or MR relay is sufiicient tomaintain this relay energized from one-half cycle to the next by thecurrent supplied to it from the bridge rectifier 1.7. The coding ratesof 75, and 180 cycles per minute are considerably slower however;consequently when the 100 per cycle per second energy is interrupted atthese rates, the code responsive relay will then drop out during eachinterrupted period. When the cycle per second energy is reinitiated theCR relay will again pick-up, consequently this relay will follow thecode which is transmitted through the track rails and induced into thereceiving coils 11 and 1-1.

It is not deemed necesary to show or explain any details re arding thedecoding apparatus 18 and the control and display apparatus 19 sincethis invention is concerned primarily with fail-safe operation of the.CR relay. Any one familiar with the former art may examine theconsiderable quantity of former patents regarding the details of thesetwo major sections of the apparatus. Furthermore, a designer for someparticular control and display system may design other apparatus thanthat shown in former patents for some specific purpose, and accordinglydesign the decoding apparatus 18 to conform with all of the necessarycoding rates involved. It is to be understood that the above mentionedinterruption rates are given by way of example only, and furthermoreeven higher coding rates than those mentioned may readily beaccommodated by the saturable reactor 16.

The waveform of FIG. 3 illustrate normal operation of the system at thestart with a fault developing later during the illustrated period;whereas FIG. 4 illustrates .and thereafter a faulty condition isrepresented.

an abnormal condition which may possibly occur and in each instance willprovide a fail-safe result.

More specifically the waveforms A through G of FIG. 3 involve normaloperation of the system for some rate of interruption of the transmittedsignal up to time T3 In waveform A of FIG. 3 a sine wave is shown whichis induced into the receiving coils 11 and 11 from the track rails andapplied to the input of the filter 34. The frequency of this waveform,as stated before, is of the order of 100 cycles per second. The actualwaveform is represented at a lower frequency than this merely forsimplification. For some period from 20 to t1 this frequency is turnedon, whereas from the time period between 11 and t2 this frequency isturned off. This cycle of application and interruption of the voltage isrepeated at the various coding rates such as 75, 120 and 180 cycles perminute so that at time t2 the waveform is again shown turned on untiltime t4.

The waveform B of FIG. 3 illustrates the output from amplifier 22 and asheretofore explained only the negative half portions of this waveformappear in the output at this point. Similarly waveform C of FIG. 3 showsthe negative half portions of the output from amplifier 23. Note thatthese two half cycles appear in time sequence, first the latter then theformer. In waveform D of FIG. 3 is represented the combined A.C. outputsfrom amplifiers 22 and 23 applied to the primary of the saturablereactor 16 with respect to ground potential. Due to the push-pullarrangement of the amplifiers 22 and 23 in connecting to the primaries24 and 25, the output from amplifier 22 will remain unaltered but theoutput from amplifier 23 will be reversed to a positive-going pulse,with respect to ground. Consequently, the portion 60 of waveform C inFIG. 3 becomes the inverse portion 61 of waveform D in FIG. 3 and theportion 63 of the waveform D remains of the same polarity as portion 62of waveform B. The combination of portions 61 and 63 of waveform Dtherefore constitute a complete in-phase cycle for operation of thesaturable reactor 16.

At some time t3 between times t2 and t4 let us assume a fault occurs inamplifier 22 such that no output or very little output results. In thewaveform B of FIG. 3 at time 23 a very small output is shown asrepresented by the voltage wave 64. In the Waveform D at time t3 theoriginal sine wave will be merely half sine Wave pulses from this pointhenceforth in the case amplifier 22 is completely open, or will be somelow amplitude sine wave such as denoted at 65, if only a small outputresults from amplifier 22. The final result of this fault will be discussed later.

The waveform E of FIG. 3 shows the change in flux in the core of thesaturable transformer 16. If we assume that the core resides in anegative state of saturation such as shown by point 66 thepositive-going pulse in waveform D will saturate the core to thepositive direction and after some time period ending at t5, for example,a certain number of volt-seconds or webers, such. as W1, will be addedto the core material. Inasmuch as the core material in this transformerhas a rectangularly shaped characteristic of hysteresis, the flux cannotchange any further at this point for the duration of this half cycle.This constant flux condition is shown by the straight horizontal line 67in the waveform E of FIG. 3. After the input waveform crosses the axisand proceeds in the negative direction, it accumulates a certain numberof negative webers as time progresses and at time t6, for example, thecore is completely saturated in the negative direction and from thispoint forward within this half cycle no additional flux can be added tothe core. When the 100 cycle per second energy is cut off at time t1 thecore will reside in the negative saturated condition where it started.

Let us now consider the result of the change in output from amplifier 22which happened at time t3 of waveform B. Just prior to this time t3, thecore has saturated in the positive direction as indicated by thestraight line segment 67 in waveform E. The portion 65'of waveform D isnot sufficiently negative to produce a quantity of webers within thenext complete half cycle to saturate the core in a negative direction,consequently for the duration of this period, and even beyond time 14,the core will remain in a positively saturated state.

In waveform F of FIG. 3 an induced current waveform flowing in thesecondary winding 26 is represented which is the result of the fluxchanges in the core 16 as shown in waveform E of FIG. 3. Whenever thecore is in the process of saturating to a positive direction apositive-going current results, and similarly whenever the flux changesin the negative direction a negative-going current results. Wheneverthere is no negative state, the current will exponentially drop to O.The portion 68 of the waveform F represents the positive-going currentcaused by a change in the flux level from the negative to a positivestate. The curve 69 represents the voltage exponentially dropping toward0 during the time after t5 when the flux saturation is at asubstantially constant level. As soon as the flux changes in thenegative direction a negative-going current is started which isrepresented by curve 70. This negative-going current will continue untilthe flux reaches the negative-state of saturation, and at that timeanother current curve 69 will be generated, for during this period thecurrent will be attempting to reach 0. Near the end of the on period theflux of waveform E becomes constant on the negative polarity side, andat this time curve 71 is generated in waveform F signifying that thecurrent after some time period drops to 0. If we do examine the point attime t3 in this same waveform F it will be noted that when thesaturation level of the flux is in the positive direction, such asindicated by curve 67 of waveform E, the current of waveform F will droptoward 0 exponentially from a positive direction as indicated by curve72.

The waveform G of FIG. 3 represents the current through the CR relay dueto the application of the current such as developed in accordance withwaveform F. After a short period of time the initial current will risesufficiently to energize the CR relay which is shown picked-up at point73 in this waveform. The inductance of the CR relay is sufiicient tocause some time delay in this circuit, consequently the inductivereactance of the relay will tend to maintain the current flow. A slightreduction in current is shown by curve 74 in this waveform F when thecurrent is tending toward 0. Even a very rapid change in current, suchas represented by curve 70 in Waveform F, will not produce a radicalchange in the curve of waveform G as shown by the curve section '76.When the current again becomes positive-going due to rectifier action ofbridge circuit 17, curve 77 will result in the current waveform, and asa result, sufficient current will be continued through the relay tomaintain it in an energized condition. It is only after the currentdrops to 0 as represented by curve 71, that the current, as representedby curve 79, will even more slowly drop to 0. At some level lower thanpoint 73 on this curve such as at 80 the CR relay will drop out. Thispoint is shown at a lower current level than that required to pick upthe CR relay, since a relay usually requires more energy for attractingits armature above that required to drop it out. In waveform G at point81 the CR relay will become deenergized due to the fault occurring inamplifier 22 at time t3, and remain henceforth deenergized until suchfault is corrected. This is one condition then under which fail-safeoperation is achieved, inasmuch as the decoding apparatus may readily bearranged so that a maintained drop out of the CR relay, rather than adrop out during a coding period, will cause the control serve to checkeach channel of the amplifiers.

and display apparatus 19 to place the locomotive in a stop condition.

The operation of the push button switches 28 and 29 across therespective receiving coils 11 and 11 in FIG. 2 Since this input alonefrom each receiving coil should be producing the input to each half ofthe primary winding of the saturable reactor 16, the elimination of eachseparately should cause the CR relay to stop pulsating at the intervalsof transmission of the pulses. More specifically, when the operatordepresses push button 28 it will shortcircuit the induced energy intothe receiving coil 11 and thereby provide no output for the upperamplifier channel in FIG. 2. This output is normally fed between groundpotential and the input capacitor 36 within the filter 34. When thisinput signal is eliminated, and providing the lower amplifier channel isWorking properly, the saturable reactor 16 will be receiving energy ofhalf-cycle pulses only in the primary winding 25. From FIG. 3 in ourformer discussion we have ascertained that this condition would resultin a positive flux saturation of core 16, and consequently the CR relaywould not operate in response to a track code. If normal operationpersists when this button 28 is depressed the operator realizes thatsuch operation is caused by some malfunction such as stray voltageswhich are causing this channel to apparently operate in a normal manner.The operator also has at his disposal push button 29 by which he maysimilarly short out the induced energy in receiving coil 11' and therebycheck whether the lower amplifier channel is really producing any inputenergy to saturate the reactor 1 Another malfunction which may occur isa short circuit in one amplifier. Let us assume that a shortcircuithaving some resistance has occurred in amplifier 22 which issufiiciently high so that the primary winding 24 will not become opencircuited from excessive heat. Rather than provide another illustration,this situation may readily be followed by referring to FIG. 3. A cathodeto plate short (not a direct short, for this'is quite uncommon) wouldcause a large negative current to flow through winding 24 in FIG. 2thereby producing a. large negative voltage which could be representedas a negative horizontal line in the curve B of FIG. 3 and having a highamplitude fore-shortened negative sine wave pulses as indicated by curve64. The effect of this high negative voltage may be thought of as ashift in the central axis of the waveform to a rather high negativeposition. The positive half wave pulses acting with reference to thisshifted axis would have no effect in changing the core saturation to thepositive side, consequently the core of the saturable reactor 16 wouldbe maintained in a negatively polarized saturated condition. This againwould result in no response from the CR relay, consequently the systemmay be said to be failsafe with respect to a short-circuit occurring inone amplifier.

In FIG. 4 waveforms A through E represent another type of malfunctionwhich produces no input to the CR relay. In waveform A of FIG. 4 theinduced track voltages are shown out of phase by 180. This energy willproduce the same output from amplifier 22 as before, consequentlywaveform B of FIG. 4 represents the sarne voltage output as that shownin waveform B of FIG. 3. Since the voltage into the other channel isreversed by 180 the output of amplifier 23, on the other hand, as shownin waveform C of FIG. 4, will be 180 out of phase with respect to thatshown in Waveform C of FIG. 3. As before the output from each of theseamplifiers is added together, consequently when the waveform B of FIG. 4is added to that of waveform C of FIG. 4 one will cancel the otherresulting in no output as represented by the dotted cancelled waveform Dof FIG. 4. It must be remembered that the waveform C of FIG. 4 isinverted due to the push-pull connection into the primary of thesaturable reactor 16. Since current input to the saturable reactor 16 isequal and opposing at all times, it will remain in its last saturatedcondition which as we assumed is usually the negative saturatedcondition. Because of this, a straight line is represented by E FIG. 4below the central axis to indicate this negative saturated condition ofthe core. This again will realize another fail-safe functioning of thesystem.

It should be noted that either polarized saturated condition causes noenergization of the CR relay, the system will remain inactivated, andconsequently the control and display apparatus 19 on the locomotive willbe placed to a stop condition.

It should be understood that although the embodiment of this inventionillustrates electron tubes for amplifiers, transistors may be used aswell. Furthermore, it should be understood that a diode clipper or otherdetection means could also be used as a substitute for the class Bamplifiers 22 and 23.

Having described a continuous inductive cab signal receiving systemcomprising a saturable reactor as one specific embodiment of the presentinvention, it is desired to be understood that this form is selected tofacilitate in the disclosure of the invention rather than to limit thenumber of forms which the invention may assume, and it is further to beunderstood that various adaptations, alterations, and modifications maybe applied to the specific form shown to meet the requirements ofpractice without in any manner departing from the spirit or scope of thepresent invention.

What I claim is:

l. A system for receiving inductively an A.C. voltage that is applied toa conducting means having a loop circuit configuration comprising;

(a) receiving means positioned in inductive relation to said conductingmeans at opposite sides of said loop circuit, each receiving means beinginductively influenced independently by the AC. voltage in itsrespective opposite side of said loop circuit;

,(b) an amplifying means electrically connected to each said receivingmeans effective to produce a pair of output signals in predeterminedphase relation when the AC. voltage in said conducting means is uniformin both sides of said loop circuit;

(c) means responsive to said pair of output signals effective to producean output corresponding to the first half cycle portion of one of saidpair of signals during the first half of each cycle of said A.C. voltageand an output corresponding to the second half cycle portion of theother one of said pair of signals during the second half of each cycleof said A.C. voltage;

(d) a transformer having a saturable core, a primary winding and asecondary winding, said primary winding effective to saturate said corefrom one predetermined state to another predetermined state in responseto a signal of predetermined amplitude during the first half of eachcycle and to saturate said core from said other state to the one statein response to a signal of predetermined amplitude during the secendhalf of each cycle, said secondary winding opera tive to produce aneffective output only while said core is changing from said onesaturated state to the other and vice versa;

(e) means operatively connecting electrically the outputs of said lastnamed .means to said primary winding to cause said primary winding tosaturate said core from said one state to saidother state in response toone of said pair of signals during the first half of each cycle and tosaturate said core from said other state to said one state in responseto said other signal during the second half or" each cycle only whensaid pair of signals are of predetermined amplitude during it V 7 theirrespective half cycle periods; and

(f) means electrically connected to said secondary winding effective tobe operated only while said secondary winding is producing an effectiveoutput.

2. A system according to claim 1 wherein said predetermined phaserelation between said output signals is 180.

3. A system for receiving inductively an A.C. voltage that is applied toa conducting means having a loop circuit configuration comprising;

(a) receiving means positioned in inductive relation to said conductingmeans at opposite sides of said loop circuit, each receiving means beingeffective to be inductively influenced independently by the A.C. voltagein its respective opposite side of said loop circuit;

(b) an amplifying means electrically connected to each said receivingmeans etfective to produce a pair of output signals of the equalamplitude and 180 out of phase relative to each other when the A.C.Voltage is uniform and of predetermined phase relation in both sides ofsaid loop circuit;

() means responsive to said pair of output signals effective to clipone-half cycle from both said output signals to produce a varying DC.voltage output;

(d) transformer means having a saturable core; a primary winding and asecondary winding, said secondary winding being operative to produce aneffective output only while said core is changing from one predetermined saturated state to the other and vice versa;

(e) means electrically connecting the output of said rectifying means tosaid primary winding effective to cause said primary winding to saturatesaid core from one state to the other in response to said varying DC.output during each first half of each cycle and to saturate said corefrom said other state to said one state in response to said varying DC.output during the second half of each cycle when the signals are ofpredetermined amplitude during both said half cycles; and

(f) means electrically connected to said secondary winding effective tobe operated only while said secondary Winding is producing an effectiveoutput.

4. A system for operating a code responsive device at a ratecorresponding to the on and off times of an A.C. voltage that is appliedacross a pair of track rails only when the A.C. voltage during the ontimes is of predetermined phase relation in both said track rails,comprising;

(a) a first receiving coil positioned to receive inductively the A.C.voltage in one of said track rails;

(b) a second receiving coil positioned to receive inductively the A.C.voltage in the other of said track rails;

(c) means operatively connected electrically to said first and secondreceiving coils effective to provide during each cycle of said A.C.voltage a first output corresponding to the A.C. voltage in one of saidtrack rails during an odd half cycle and a second output correspondingto the A.C. voltage in the other track rail during the even half cycle;

(d) a saturable transformer having a primary and a secondary winding anda saturable core, said secondary winding being operative to produce aneffective output only when said core is changing from one predeterminedstate to another predetermined state and vice versa;

(e) circuit means electrically connecting operatively the first andsecond outputs from said last named means to the primary winding tocause said core to saturate from said one state to said other state inresponse to the first output of predetermined amplitude in the odd halfof each cycle when said core is in said one state at the beginning ofsaid odd half cycle and to cause said core to saturate from said otherstate to said one state in response to the second output ofpredetermined amplitude in the even half of each cycle when said core isin said other state at the beginning of said even half cycle;

(f) and code responsive means electrically connected to said secondarywinding and responsive to an effective output therefrom.

5. A train control system of the continuous inductive type for railroadswherein an A.C. voltage is applied across the track rails to havedistinctive on and off periods at different selected rates in accordancewith traffic conditions, comprising:

(a) a first train carried receiving coil positioned in inductiverelation with one track rail to receive inductively the A.C. voltage insaid one rail;

(b) a second train carried receiving coil positioned in inductiverelation with the other track rail to receive inductively the A.C.voltage in said other rail;

(0) a saturable reactor on the train including a primary winding and asecondary winding and a saturable core, said secondary winding beingoperative to produce an effective output only when said saturable coreis being operated from one predetermined saturated state to anotherpredetermined saturated state and from said other state to said onestate by an A.C. voltage applied to said primary winding of apredetermined phase and amplitude;

(d) means electrically connecting operatively both said receiving coilsto said primary winding effective to induce an A.C. voltage in said corecharacteristic of the A.C. voltage in said one rail during the firsthalf of each cycle and characteristic of the A.C. voltage in the otherrail during the second half of each cycle, whereby said secondarywinding provides an effective output only when the A.C. voltage in bothsaid track rails are of a predetermined amplitude and in predeterminedphase relation; and

(e) train governing apparatus operatively connected to said secondarywinding effective to be operated in response to an effective output fromsaid secondary winding.

6. A train control system of the continuous inductive type for railroadswherein an A.C. voltage is applied across the track rails to havedistinctive on and off" periods at different selected rates inaccordance with trafiic conditions, comprising:

(a) a first train carried receiving coil positioned in inductiverelation with one track rail to receive inductively the A.C. voltage inone of said rails;

(b) a second train carried receiving coil positioned in inductiverelation with the other track rail to receive inductively the A.C.voltage in the other of said rails;

(c) amplifying and clipping means electrically connected operatively toeach of said receiving coils effective to amplify said inducted A.C.voltage in each of said coils independently and to clip one polarity ofeach of said A.C. voltages;

(d) a saturable reactor having a primary and secondary winding and asaturable core;

(e) means including said primary winding electrically connected to theoutput of said amplification and clipping means effective to invert theclipped signal from said first receiving coil and combining saidinverted signal with the amplified and clipped signal from said secondreceiving coil to produce a continuous waveform in said primary windingcharacteristic of the A.C. voltage flowing in both said track rails;

(f) said core being operative to saturate from one predetermined stateto the other predetermined state and from said other state to said onestate in response to the waveform applied to said primary winding onlywhen the waveform of each half cycle is in predetermined phaserelationship and of a predetermined amplitude;

(g) said secondary winding being operative to produce an effectiveoutput only when said core is changing from one saturated state to theother and vice versa;

(h) and means connected to said secondary Winding operative in responseto an eifective output from said secondary winding only.

7. A train control system of the continuous inductive type for railroadswherein an A.C. voltage is applied across the track rails to havedistinctive on and off periods at different selected rates in accordancewith ,"trafiic conditions, comprising:

(a) a first train carried receiving coil positioned in inductiverelation with one track rail to receive inductively the A.C. voltage insaid one rail;

([7) a second train carried receiving coil positioned in inductiverelation with the other track rail to receive inductively the A.C.voltage in said other rail;

() an amplifying means electrically connected operatively to each ofsaid receiving coils eifective to produce a pair of amplified outputsignals of equal amplitude and 180 out of phase relative to each otherwhen the A.C. voltage in both said track rails is uniform and ofpredetermined phase relation;

(d) means responsive to said pair of output signals efiective to clipone-half cycle from both said output signals to produce a varying DC.voltage output;

(2) transformer means having a primary winding and a secondary Windingand a saturable core, said secondary winding being operative to producean effective output only while said core is changing from onepredetermined saturated state to the other and vice versa,

(f) means electrically connecting the output of said rectifying means tosaid primary winding effective to cause said primary winding to saturatesaid core from said one state to the other in response to the 14 varyingDC. voltage during the first half of each cycle and to saturate saidcore from said other state to said one state in response to the varyingDC.

voltage during the second half of each cycle when both said half cyclesare uniform; and

(g) means electrically connected to said secondary winding effective tobe operated only While said secondary winding is producing an effectiveoutput, whereby said last mentioned means is operated in response to theA.C. voltage across said track rails only when said A.C. voltage in onetrack rail is in proper phase relation with the A.C. voltage in theother track rail and the amplitude of the voltage in both said trackrails is uniform.

8. A system according to claim 7 wherein said first and second receivingcoils are connected in series and said amplifying means includes a classA amplifier having an output for each of said receiving coils.

9. A system according to claim 8 wherein said clipping means includes aclass B amplifier effective to clip one polarity of each output fromsaid class A amplifier during adjacent half cycles.

References Cited in the file of this patent UNITED STATES PATENTS1,704,110 Snavely Mar. 5, 1929 2,054,676 La Pierre Sept. 15, 19362,197,414 Place Apr. 16, 1940 2,649,557 Ransom Aug. 18, 1953 2,676,253Ayres Apr. 20, 1954 2,731,550 Stafford Jan. 17, 1956 2,731,553 Zaifaranoet al Jan. 17, 1956 2,781,479 Rice Feb. 12, 1957 2,959,670 Kendall eta1. Nov. 8, 1960 2,982,851 Maenpaa May 2, 1961 3,030,521 Lucke Apr. 17,1962

1. A SYSTEM FOR RECEIVING INDUCTIVELY AN A.C. VOLTAGE THAT IS APPLIED TOA CONDUCTING MEANS HAVING A LOOP CIRUCIT CONFIGURATION COMPRISING; (A)RECEIVING MEANS POSITIONED IN INDUCTIVE RELATION TO SAID CONDUCTINGMEANS AT OPPOSITE SIDES OF SAID LOOP CIRCUIT, EACH RECEIVING MEANS BEINGINDUCTIVELY INFLUENCED INDEPENDENTLY BY THE A.C. VOLTAGE IN ITSRESPECTIVE OPPOSITE SIDE OF SAID LOOP CIRCUIT; (B) AN AMPLIFYING MEANSELECTRICALLY CONNECTED TO EACH SAID RECEIVING MEANS EFFECTIVE TO PRODUCEA PAIR OF OUTPUT SIGNALS IN PREDETERMINED PHASE RELATION WHEN THE A.C.VOLTAGE IN SAID CONDUCTING MEANS IS UNIFORM IN BOTH SIDES OF SAID LOOPCIRCUIT; (C) MEANS RESPONSIVE TO SAID PAIR OF OUTPUT SIGNALS EFFECTIVETO PRODUCE AN OUTPUT CORRESPONDING TO THE FIRST HALF CYCLE PORTRION OFONE OF SAID PAIR OF SIGNALS DURING THE FIRST HALF OF EACH CYCLE OF SAIDA.C. VOLTAGE AND AN OUTPUT CORRESPONDING TO THE SECOND HALF CYCLEPORTION OF THE OTHER ONE OF SAID PAIR OF SIGNALS DURING SECOND HALF OFEACH CYCLE OF SAID A.C. THE VOLTAGE (D) A TRANSFORMER HAVING A SATURABLECORE, A PRIMARY WINDING AND A SECONDARY WINDING, SAID PRIMARY WINDINGEFFECTIVE TO SATURATE SAID CORE FROM ONE PREDETERMINED STATE TO ANOTHERPREDETERMINED STATE IN RESPONSE TO A SIGNAL OF PREDETERMINED AMPLITUDEDURING THE FIRST HALF OF EACH CYCLE AND TO SATURATE SAID CORE FROM SAIDOTHER STATE TO THE ONE STATE IN RESPONSE TO A SIGNAL OF PREDETERMINEDAMPLITUDE DURING THE SECOND HALF OF EACH CYCLE, SAID SECONDARY WINDINGOPERATIVE TO PRODUCE AN EFFECTIVE OUTPUT ONLY WHILE SAID CORE ISCHANGING FROM SAID ONE SATURATED STATE TO THE OTHER AND VICE VERSA;